Great feedback. Hadn’t mentioned that, and the smaller ID could be a concern for some. I wonder, though, if the manifold design renders most of that reduced flow moot? That would be a cool study or test…Might even be solved mathematically. We’ll check into it!

P.S. When comparing nominal pipe sizes, PEX actually has a significantly smaller ID than copper and some types of PVC. Although not widely reported, this does decrease flow when compared to “soft wall” copper. For example, the ID of nominal 1″ PEX is equivalent to nominal 3/4″ copper. Once you need a 1-1/4″ ID pipe, PEX can become expensive indeed!

Clint- I want to note that copper is not always significantly more expensive than PEX, depending on pipe diameter. From 1/2″-1″ pipes, PEX is the clear winner. Once you get to 1-1/4″-1-1/2″ copper is often only just a few % more expensive. Large PEX crimpers get very expensive and large PEX pipe is not readily available. When you hit 2″, PVC is often the only economical solution.

-Another major problem with PEX is that it’s vulnerable to hungry rats. I wouldn’t use it without a protective sleeve in crawl spaces.